Unsaturated compounds have carbon-carbon double bonds. These compounds exist in either the cis or the trans configuration. Specifically unsaturated compounds containing functional groups having C═O are technically very important and have different properties depending on which double bond isomer (cis or trans) is present in the corresponding compound. These compounds are particularly important for the fields of flavours and fragrances, pharmaceutical compositions and the synthesis of vitamins, particularly of vitamin K1 as well as tocopherols. The isomers particularly differ in odour as well as in their behaviour towards asymmetric additions to the respective carbon-carbon double bond.
It is known that carbon-carbon double bonds can be isomerized. EP 0 858 986 A1 discloses a process to isomerize vitamin A compounds having a system of polyconjugated carbon-carbon double bonds (—C═C—C═C—C═C—C═C—C═C—) by nitrogen monoxide. It is, however, known that compounds having isolated (non-conjugated) double bonds strongly differ in their behavior, particularly reactivity, compared to behave strongly different than compounds having polyconjugated carbon-carbon bonds.